The invention relates to optical systems and, in particular, to procedures for aligning the optical axes of the systems relative to their mounting surfaces.
Optical systems, such as automatic astronomical telescopes or the like, usually are mounted on support surfaces or plates and, for accurate results, the optical axes should lie at a precise angle relative to the mounting surface. This angle is known as the alignment angle and, prior to use of the optics, it must be carefully checked to determine with a high degree of accuracy any deviations that may exist. Deviations then can be corrected by re-adjusting the mounting. Alternatively, minor deviations can be accommodated in the computer which normally is used with these automatic telescopes.
Conventionally, alignment measurements are accomplished by generating an optical reference beam of known orientation and measuring the deviation of the image formed by the beam in the optical system from its center when the mounting surface is carefully leveled. The errors associated with this procedure generally are acceptable because it is possible to level a surface quite accurately by, for example, rotating it about a vertical axis or by the use of pendulous prisms to provide a reference orientation. There are, however, certain problems associated with such procedures. For example, the auxiliary test equipment used in the measurements can introduce errors. Further, the prior procedures rely somewhat upon the techniques and skills of the individual observers. Experience also has shown that even the movements of these observers around the test equipment can introduce errors in the measurements. In general, the achievement of the highest possible precision requires the elimination of the test equipment as well as the use of a procedure which eliminates the need for operating personnel in the immediate area.
It is therefore an object of the present invention to provide a fully automated procedure for measuring the so-called alignment angles as well as a procedure which eliminates as much as possible the need for auxiliary test equipment.
The purposes of the present invention fundamentally are achieved by employing a scanning technique capable of detecting deviations of focal plane images from fixed positions which obtain when the alignment of the optical axis relative to its mounting surface is true. The scanner is a part of a vidicon or its solid state equivalent which conventionally is a unitary part of such optical systems as the automatic astronomical telescopes. The vidicon itself includes an image-storing face plate disposed in the focal plane of the optics. Diffuse reflectors are arranged in predetermined positions on the face plate to project light through the optics onto a liquid pool which, in turn, reflects the light as images back to certain fixed locations on the face plate. For this purpose, the diffuse reflector arrangement is such that the images fall onto dark or unilluminated surface areas of the plate. Scanning determines the relative location of both the images and their reflector sources so that deviations of the images from their aligned positions can be measured.